My understanding was that M-Pesa started as a domestic remittance solution. Kenya doesn't have a well developed ATM network, so there was a great need for simple and secure domestic remittances (send money home to your family every week type use-cases).
The remittance solution replaced existing methods like sending physical cash with an "agent" (e.g. taxi driver) at high cost/risk or driving/walking very far to a bank branch.
Once the remittance use-case was established, payments was an easy addition, as there was already value flowing through the system.
Though, the only benefit they have compared to cash is that you can transmit the numbers over the phone.
What would the bar manager do with 1 million minutes of talk time? [serious]
You're not surprised that a bar manager manages to find something to do with more alcohol than he could possibly drink, right?